The invention relates to a process for production of an ink knife for an ink duct roller of a printing machine from a metal plate at least 2 mm thick, where parallel slots are formed which extend at right angles from the working edge of the ink knife over part of the plate width and form blades of ink zone width.
Multiple-blade ink knives are known for example from CH-A5 602345. This ink knife has in the area of the working edge recesses which lie on both sides of adjustment screws next to the blades. The blades can be adjusted individually, a mechanical influence on the adjacent blade area is excluded or at least substantially reduced. The thickness of the ink layer can be set on each blade, individual ink amounts in the different ink zones can be changed as required by the printing image in the different ink zone widths. The disadvantage of this solution is the intermediate spaces between the blades which allow the passage of even high viscosity inks and the formation of annular rings on the ink ductor.
According to the known state of the art, various measures are proposed which prevent at least in part the penetration of ink into the slots but always entail other disadvantages.
According to DE, A1 2228625, the slots between the blades of an ink knife are filled with a plastic. This mechanically decouples adjacent blades thanks to the elasticity of the plastic. As the usage period increases however there is an increasing risk that parts of the plastic, in particular when a blade is greatly deflected in comparison with its neighbor, will come loose and harm the print quality.
Numerous design forms are known according to which the slots between the blades of an ink knife are covered either with a metal or with a plastic foil, for example according to U.S. Pat. No. 2837024. These cover foils are effective but cause substantial problems for example as a result of wear and penetration of the ink between the foil and the blades.
In DE, C1 3525589, the working edge of an ink knife is slotted with a wire erosion machine or with laser beams. An adhesive coating of a material softer than the ink knife has a greater thickness than the width of the slot. When the blade is adjusted, the excess material is cut away and the slot completely closed. The penetration of ink into the narrow slot is prevented with complex measures.
According to EP, B1 0376885, ink knives are produced which have slots formed by laser beams of a width of 0.1 to 0.3 mm, which prevents leakage without additional cover in the case of high viscosity printing inks. In addition to the defined slot widths, the ink knife must have the following properties:
The slots must be longer than half the plate width but must not exceed two-thirds thereof. PA1 The thickness of the plate must be at least twice the maximum adjustment path of the blades. PA1 (a) blind-ended, parallel, transverse grooves are cut out of the metal plate at intervals corresponding to the ink zone width, starting from the working edge, and PA1 (b) the metal plate is cut through in the area of the transverse grooves to form a narrow slot at intervals corresponding to the ink zone width.
Preferred plate thicknesses are 1 to 3 mm. It has been shown that in the thicker plate range extremely narrow slots from 0.01 to 0.03 mm width can only be cut out cleanly and regularly with great difficulty, if at all. Furthermore this solution is limited to high viscosity inks.